Problem: Simplify the following expression: $n = \dfrac{-9}{4r} - \dfrac{-3}{4r}$
Since the expressions have the same denominator we simply combine the numerators: $n = \dfrac{-9 - (-3)}{4r}$ Combine like terms: $n = \dfrac{-6}{4r}$ Simplify by dividing numerator and denominator by 2: $n = \dfrac{-3}{2r}$